John Stagliano is considered to have started the gonzo pornography genre with his Buttman series of films. The naked appearance of actress Demi Moore in the advanced stage of pregnancy on the cover of Vanity Fair magazine in 1991 marked the beginning of a period which has since seen pregnancy presented by celebrities as a glamorous state of living, while also creating a market for photographers to produce images of pregnant mothers, and for fashion 3d hentai stylists to introduce pregnancy styling to their business. The volume of semen that is ejaculated depends on several factors, including the male health, age, degree of sexual excitement, and the time since his last ejaculation. Voyeur pornography may also include shots of topless women on topless beaches who are unaware of the cameras but may legally be photographed due to the public setting. These styles are much closer to the style of bondage scenes mature milfs in mainstream television. Clothed female, naked male pornography features naked men and clothed women; typically, the women humiliate and abuse the men or perform fellatio and/or handjobs on the men. Interactive pornography, available in CD-ROM and DVD format, allows the viewer to select the particular acts performed at any one time, sometimes with the camera providing a first person view. Studies have found that masturbation is frequent in humans of both sexes and all ages, although there is variation. Hardcore pornography is pornography that depicts penetration or extreme fetish acts, or both. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. Sexual orientation Pornography features an increasing variety of combinations of actors by their sexual gay twink porn orientation such as lesbian, gay, bisexual, and transsexuals in addition to traditional heterosexual roles.